A variety of ferrules have been developed to facilitate the interconnection of optical fibers, with other optical fibers, optical devices or the like. For example, a number of standard ferrules, such as SC, FC, and ST ferrules, have been designed. Regardless of their type, ferrules typically define one or more longitudinal extending bores for receiving end portions of respective optical fibers.
One common type of ferrule is an APC ferrule that is designed to make physical conduct with another APC ferrule during the process of interconnecting a pair of optical fibers. Notably, the front face of an APC ferrule is disposed at a nonorthogonal angle, i.e., at other than 90°, relative to the longitudinal axis defined by the ferrule. For example, the front face of an APC ferrule is commonly disposed at an angle of approximately 8° relative to a plane that extends perpendicular to the longitudinal axis defined by the ferrule. In order to interconnect a pair of APC ferrules, the ferrules are therefore positioned such that the angled front faces are complimentary to one another, that is, the forwardmost portion of the front face of one ferrule is preferably aligned with the rearwardmost portion of the front face of the other ferrule and vice versa. In order to facilitate the alignment of the ferrules in this complimentary fashion, the ferrules typically include a key that is disposed in a predetermined relationship to the front face of the ferrule. Thus, a connector sleeve or the like can be utilized to engage the keys of a pair of APC ferrules to insure that the ferrules are mated in a complementary fashion.
The angled front face of an APC ferrule advantageously reduces undesirable reflections of optical signals at the interface between a pair of optical fibers, thereby decreasing optical power losses and correspondingly increasing optical power transmission. In addition to forming the ferrule to have a front face that is disposed at a predetermined angle relative to the longitudinal axis defined by the ferrule, the front face of some APC ferrules has a spherical shape. In this regard, if an APC ferrule is constructed such that the apex of the spherical surface substantially coincides with the bore defined by the ferrule, physical contact between the end portions of the respective optical fibers is facilitated, thereby enhancing optical transmission between the optical fibers. Unfortunately, it is relatively difficult to shape the spherical surface of an APC ferrule such that the apex of the spherical surface coincides with the bore defined by the ferrule. Instead, APC ferrules having a spherical front face generally have an apex offset that is defined as the distance by which the apex of the spherical surface is offset from the bore defined by the ferrule. While some apex offset can be tolerated while still maintaining optical transmission between the respective optical fibers, signal transmission can be adversely impacted if the apex offset becomes too large, such as greater than 50 microns. The degree of apex offset that can be tolerated is dependent upon several factors including whether the optical fibers are single mode or multimode, as well as the radius of curvature of the spherical surface. In this regard, greater apex offsets are typically acceptable for spherical surfaces having larger radii of curvature than for spherical surfaces having smaller radii of curvature.
Conventional APC ferrules that are to include a spherical front face typically require that the amount of material that is removed from the front face of the ferrule to define the spherical surface be precisely controlled so as to form the spherical surface in such a manner that the apex of the spherical surface coincides with the bore defined by the ferrule. In this regard, the removal of either too much or too little material during the process of grinding the front face of an APC ferrule into a spherical shape would typically result in the apex of the spherical surface being offset from the bore defined by the ferrule. In an attempt to minimize the apex effect, at least some of the prior techniques for grinding the front face of an APC ferrule to define the spherical surface are relatively complex, thereby decreasing the efficiency and increasing the cost at which APC ferrules can be fabricated.
One exemplary APC ferrule is described by U.S. Pat. No. 5,351,327 along with several techniques for fabricating the APC ferrule. As described, the APC ferrule has a spherically shaped front face with an apex offset of no more than 50 microns and, more typically, no more than 10 microns. While several different fabrication techniques are described, most of the techniques require that the front face of the ferrule be formed into a temporary surface that is then repolished to form the desired spherical surface. The temporary surface can be either flat or spherical and is typically angled or inclined relative to a plane perpendicular to the longitudinal axis defined by the ferrule. Unfortunately, the repolishing of the front face and the other finishing operations disadvantageously consume polishing consumables and reduce the efficiency with which the ferrules can be fabricated.
In addition, U.S. Pat. No. 5,148,660 describes an APC ferrule having a spherical front surface that is angled relative to a plane perpendicular to the longitudinal axis defined by the ferrule. The APC ferrule described by U.S. Pat. No. 5,140,660 includes a cylindrical tip or pedestal that extends forwardly from the main portion of the ferrule body and that has a smaller diameter than the main portion of the ferrule body. As such, the cylindrical tip may damage surfaces that come into contact with the front face of the ferrule, such as by tearing polishing film or cleaning clothes.
While a number of APC ferrules have therefore been proposed that include spherical front faces, each of these conventional APC ferrules is subject to some shortcomings. For example, the process of grinding the front face of the ferrule may have to be closely monitored since the removal of too much or too little material may disadvantageously increase the apex offset. In addition, some APC ferrules may require extensive polishing or other finishing operations such that the front face is sufficiently smooth, thereby increasing the fabrication costs and the resulting cost of the APC ferrules. Thus, with increasing emphasis being placed upon lowering the cost of ferrules and reducing the permissible tolerances of the ferrules, an improved APC ferrule is desired that offers a reduced apex offset and that can be fabricated in a relatively simple fashion, thereby reducing fabrication costs and the cost of the resulting APC ferrules relative to conventional fabrication techniques.